The present invention relates to a method for the preparation of diaminoresorcinol.
4,6-Diaminoresorcinol is a monomer used in preparing polybenzoxazoles (PBO). Although there are a number of known methods for preparing 4,6-diaminoresorcinol, there continues to be a need to find more efficient and cost effective routes to obtain 4,6-diaminoresorcinol.
One known method involves synthesizing the monomer from 1,2,3-trichlorobenzene as described in U.S. Pat. No. 4,766,244 issued to Lysenko. However, 1,2,3-trichlorobenzene has limited availability.
Another method for preparing 4,6-diaminoresorcinol involves treating 1,3-dichloro-4,6-dinitrobenzene with base, to form 4,6-dinitroresorcinol. Although 4,6-dinitroresorcinol may be reduced to form 4,6-diaminoresorcinol, the product recovery is prohibitively low for commercial value.
In yet another method, the appropriate arylether such as di-arylmethoxy-dinitrobenzene can be cleaved to produce 4,6-diaminoresorcinol. U.S. Pat. No. 5,072,053, issued to Blank et al., describes cleaving arylethers by converting di-arylmethoxydinitrobenzenes to 4,6-diaminoresorcinol by catalytic reduction using a platinum metal supported catalyst, which cleaves the diethers and reduces the nitro groups to amines. However, the method also produces toluene as an unwanted by-product which must be removed or converted back to benzyl alcohol for recycle.
Accordingly, it remains highly desirable to provide a method for preparing 4,6-diaminoresorcinol which does not have the foregoing disadvantages.